The present invention relates to a vibration generating method and device and, more particularly, to a method and device for generating vibrations in a well borehole to remove a region of reduced permeability and to increase filtration rate through porous media thereby increasing fluid recovery, production and/or injection from and/or into fluid bearing formations.
The acoustic or vibration stimulation of wells is a known technique for enhancing oil production and recovery from oil-bearing strata as is described in: xe2x80x9cElastic-Wave Stimulation of Oil Production: A Review of Methods and Resultsxe2x80x9d, Geophysics Vol.59 No. 6 (June 1994).
Various methods and apparatuses for imparting vibrations to a well in order to clean the near well zone or remove a region of reduced permeability are known in patented prior art.
U.S. Pat. No. 5,282,508, for example, refers to a formation stimulation method that simultaneously: (a) reduces the adherence forces in the layer between oil-water and the rock formation by superimposing elastic sound waves created by a sonic source installed in the well, while (b) applying an oscillating electrical stimulation of the stimulated wellbore region. One disadvantage of this invention is that it requires a continuous application of substantial quantities of energy to heat the near-well zone.
A disadvantage of prior art is use of non-eigen vibration frequency. The eigen frequency of a given porous media is defined as that frequency generated by the flow of fluid through the given porous media. Typically, it not a single frequency rather it is a spectrum of frequencies or a bandwidth. The bandwidth results from the fact that porous media is non-uniform in structure and pore size. The eigen frequency/bandwidth is often referred to as the eigen filtration frequency. Under conditions of non-eigen frequency vibrational stimulation it is impossible to reach the resonance phenomenon observed for filtration processes in fluid saturated porous media. The method for determining the filtration eigen frequency is found for example in USSR Pat. No. 1,477,900. For example, the eigen frequency of calcium carbonate formations lies in the bandwidth of 0.5-2.5 kHz (kilohertz) and the eigen frequency of sandstone formations lies in the bandwidth of 1.5-20 kHz. The eigen frequency of any given porous media depends on pressure, permeability, porosity, oil/water saturation, and oil/water properties.
The USSR Pat. No. 1,595,061 discloses a method and apparatus wherein a so-called hydrodynamic wave generator is arranged at the end of tubing and is installed into a wellbore opposite to the productive sub-layer having a region of reduced permeability due to contamination by drilling mud, fines, sand, etc. The other end of the tubing is connected to a pump in turn connected to a tank holding a liquid (e.g. water or crude oil).
The tank is connected to the wellbore casing inside which is installed the tubing, thereby providing the possibility of circulating the liquid in the system loop containing, in order: the pump, tubing, hydrodynamic wave generator, casing, tank, and returning again to the pump. The hydrodynamic wave generator creates high frequency vibrations that remove the region of reduced permeability. However, like all prior art, this method describes stimulation under conditions of non-resonance between the eigen frequency of the formation and the stimulation frequency of hydrodynamic wave generator.
Attention is also invited to U.S. Pat. Nos. 2,670,801; 3,378,075; 3,754,598; 4,049,053; 4,437,518.
The present invention was developed to overcome these and other drawbacks of prior methods by providing an improved method for the resonant stimulation of the near well zone of well.
The method in accordance with invention includes the measurement of the eigen frequencies of the filtration process in a productive reservoir by means of the downhole sensor installed on the depth of the productive layer in the active injection/producer well, installation of the vibration source (so-called wave generator) at the depth of productive layer/sublayer which is needed to be stimulated, installation of the vibration sensor in the vicinity of source of vibration and the performing the stimulation of the productive layer/sublayer on the vibration frequency corresponding the eigen frequency of the productive layer/sublayer which is needed to be stimulated. The stimulation frequency of the vibration source is measured by the vibration sensor and is transmitted to the surface in order to tune the vibration source to the eigen frequency of formation. An advantage of the present invention is that the stimulation of the productive layer/sublayer(s) is performed under the conditions of resonance thereby essentially increasing the mobility of fluid in the saturated porous medium of the productive formation, thereby substantially improving the cleaning action of vibration hence increasing the ability to produce, recover, and/or inject fluids.